This invention relates to airbag fabrics, and more particularly, to high strength, uncoated, uncalendered airbag fabric that is lighter in weight than heretofore.
In the last several years, the use of airbags as safety restraints in automobiles has become prevalent and will be standard equipment on all cars within the next few years. Airbags typically used in restraint systems in automobiles and other vehicles must satisfy a number of unique and demanding requirements. For example, airbags must have the ability to inflate fully in milliseconds, absorb the impact of the passenger, yet deflate rapidly to provide pneumatic dampening, thus preventing the passenger from being repelled in a rearward direction. Additionally, the airbag fabric must be sufficiently low in air permeability that the gases released to inflate the bag do not penetrate the fabric and blow into the face of the occupant. To operate in this matter, fabrics for use in airbag construction should be lightweight but strong, relatively airtight, packable or foldable into a confined area, and resistant to abrasion. Thus, the characteristics or parameters which are important for airbag fabrics include low air permeability, low weight, low thickness, and high strength.
Earlier fabrics for airbag construction achieved low air permeability by coating the fabric with a rubber such as chloroprene. Such coated fabrics used in the construction of airbags have several disadvantages. In addition to the higher cost of coating, the coating of a fabric adds both thickness and weight to the product which increases the space requirements for the airbag in the folded condition, which may be a very important consideration. Rubber coated fabrics may also have a tendency to stick or block during the long term compressed storage of the bag, which can be a serious drawback. In order to prevent sticking of the layers, the coated layer is often treated with talc or other treatments, which also increases the costs. Further, some fabric coatings may increase the tendency of the fabric to become brittle, which would provide for a shorter life expectancy.
In the last several years, alternatives to coating have been sought. The first alternative is a fabric which achieves low air permeability by utilizing fibers which are heat shrinkable. Once the fabric is formed, the fibers are heat shrunk, heat-set, and optionally calendared to achieve the low air permeabilities necessary. Even with calendering, the weave construction must be rather dense and this leads to a heavier construction. The calendering operation is an additional operation which adds to the cost of the fabric.
One approach to an uncoated fabric for airbags is described in U.S. Pat. No. 5,093,163. In this approach, the airbag fabric is formed from heat shrinkable, synthetic filament yarns woven in thread counts of more than 56 threads per inch. After heat shrinkage, there results a very dense and heavy fabric.
Another attempt to provide an uncoated fabric for airbags is described in U.S. Pat. No. 5,236,775 issued Aug. 17, 1993. The fabric described in the '775 patent is woven on conventional weaving equipment with thread counts again in excess of 56 threads per inch with approximately 65 threads per inch being preferred. No heat setting, shrinking, or calendering is contemplated, however, again, this is obviously a relatively dense, heavy fabric.